1. Field of the Invention
This invention relates generally to overload protection and starting relays for explosion resistant motors, and more particularly to an explosion resistant mounting for an inherent thermal overload device and starting relay for an explosion resistant hermetic motor.
2. Description of the Prior Art
Conventional hermetic motors which drive a refrigeration compressor with the compressor and motor being hermetically sealed in a common enclosure may have a thermal overload device and, in the case of single phase motors, a starting relay mounted on the casing. There are instances, however, where an explosion resistant compressor system is required for use in a hazardous atmosphere, such as in hospitals. In any explosion resistant or hazardous duty application, electrical contacts and any electrical connection which can become loosened must be housed in an explosion resistant enclosure. In prior explosion resistant refrigeration motor-compressor systems, a current-responsive overload device and, in the case of single phase systems, a motor starting relay has been remotely located in a non-explosive environment, and connected to the hermetic motor by leads enclosed in rigid pipe welded to the motor-compressor casing. In such an installation, however, the overload device senses an excessive current condition only, and does not sense excessive motor temperature. Furthermore, additional expense is involved in installation of the remotely located overload device and starting relay.
It is therefor desirable to provide inherent thermal overload protection, i.e., responsive to both temperature and current, for an explosion resistant motor, particularly an explosion resistant hermetic motor-compressor combination, and it is further desirable that thermal overload protection be provided by a commercially available thermal overload protector, simply mounted, along with a commercially available starting relay, in an explosion resistant housing readily attached to the casing of an explosion resistant motor.